#!/bin/sh
set -e

usage () {
    echo "usage: git cleanup [-lr] [-nsvh]" >&2
    echo >&2
    echo "Deletes all branches that have already been merged into the main branch." >&2
    echo "Removes those branches both locally or in the origin remote (or both)." >&2
    echo "Will be most conservative with deletions." >&2
    echo >&2
    echo "Minimally requires either (or both) of these flags to be set:" >&2
    echo "-l    Remove local branches" >&2
    echo "-r    Remove remote branches (in \`origin\`)" >&2
    echo >&2
    echo "Options:" >&2
    echo "-n    Dry-run" >&2
    echo "-s    Also consider squash merges (implies -l)" >&2
    echo "-v    Be verbose (show what's skipped)" >&2
    echo "-h    Show this help" >&2
}

dryrun=0
locals=0
remotes=0
squashed=0
verbose=0
while getopts nlrsvh flag; do
    case "$flag" in
        n) dryrun=1;;
        l) locals=1;;
        r) remotes=1;;
        s) squashed=1; locals=1;;
        v) verbose=1;;
        h) usage; exit 2;;
    esac
done
shift $(($OPTIND - 1))

if [ $remotes -eq 0 ] && [ $locals -eq 0 ]; then
    usage
    exit 1
fi

#
# This will clean up any branch (both locally and remotely) that has been
# merged into any of the known "trunks".  Trunks are any of:
#
#   - main (local) + origin/main
#   - master (local) + origin/master
#

safegit () {
    if [ "$dryrun" -eq 1 ]; then
        echo git "$@"
    else
        git "$@"
    fi
}

#
# The Algorithm[tm]:
# - Find the smallest set of common ancestors for those trunks.  (There can
#   actually be multiple, although unlikely.)
# - For each local branch, check if any of the common ancestors contains it,
#   but not vice-versa (prevents newly-created branches from being deleted)
# - Idem for each remote branch
#

find_common_base () {
    if [ $# -eq 1 ]; then
        git sha "$1"
    else
        git merge-base "$1" "$2"
    fi
}

find_branch_base () {
    branch="$1"
    base_point=""

    if git local-branch-exists "$branch"; then
        base_point=$(find_common_base "$branch" $base_point)
    fi

    if git remote-branch-exists origin "$branch"; then
        base_point=$(find_common_base "origin/$branch" $base_point)
    fi

    if [ -n "$base_point" ]; then
        echo "$base_point"
    fi
}

main="$(git main-branch)"

find_bases () {
    find_branch_base "$main"
}

bases=$(find_bases)

#
# The Clean Squashed Algorithm[tm]
# - Create a temporary dangling squashed commit with git commit-tree
# - Then use git cherry to check if the squashed commit has already been
#   applied to the main branch
# - If it has, then delete the branch
#

clean_squashed () {
    branch="$1"

    # Find the merge base for this branch
    merge_base=$(git merge-base "$main" "$branch")

    # Get the tree object of the branch
    branch_tree="$(git rev-parse "$branch^{tree}")"

    # Create a squashed commit object of the branch tree with parent
    # of $base with a commit message of "_"
    dangling_squashed_commit="$(git commit-tree "$branch_tree" -p "$merge_base" -m _)"

    # Show a summary of what has yet to be applied
    cherry_commit="$(git cherry "$main" "$dangling_squashed_commit")"

    if [ "$cherry_commit" = "- $dangling_squashed_commit" ]; then
        # If "- <commit-sha>", (ex. - "- 851cb44727") this means the
        # commit is in main and can be dropped if you rebased
        # against main
        safegit branch -D "$branch"
    elif [ $verbose -eq 1 ]; then
        # If "+ <commit-sha>", (ex. - "+ 851cb44727") this means the
        # commit still needs to be kept so that it will be applied to
        # main
        echo "Skipped $branch (no similar squash found)"
    fi
}

if [ $locals -eq 1 ]; then
    for branch in $(git local-branches \
                    | grep -vxF "$main"); do
        for base in $bases; do
            if git contains "$base" "$branch"; then
                if ! git contains "$branch" "$base"; then
                    # Actually delete
                    if ! safegit branch -D "$branch"; then
                        echo "Errors deleting local branch $branch" >&2
                    fi
                    break
                fi
            else
                # This is the case where the branches are in fact legit
                # local WIP branches or they are squashed merges, and we
                # need to check if they have been squashed-merged into
                # main. NOTE - this assumes main is up-to-date locally
                if [ "$squashed" -eq 1 ]; then
                    clean_squashed "$branch"
                fi
            fi
        done
    done
fi

# Pruning first will remove any remote tracking branches that don't exist in
# the remote anymore anyway.
if [ $remotes -eq 1 ]; then
    remote=origin
    safegit remote prune "$remote" >/dev/null 2>/dev/null

    if [ $remotes -eq 1 ]; then
        branches_to_remove=""
        for branch in $(git remote-branches "$remote" | grep -vEe "/($main)\$"); do
            for base in $bases; do
                if git contains "$base" "$branch"; then
                    if ! git contains "$branch" "$base"; then
                        branchname=$(echo "$branch" | cut -d/ -f2-)
                        branches_to_remove="$branches_to_remove $branchname"
                        break
                    fi
                fi
            done
        done

        if [ -n "$branches_to_remove" ]; then
            if ! safegit push "$remote" --delete $branches_to_remove; then
                echo "Errors deleting branches $branches_to_remove from remote '$remote'" >&2
            fi
        fi
    fi
fi

# Delete any remaining local remote-tracking branches of remotes that are gone.
if [ $locals -eq 1 ]; then
    branches_to_remove=""
    for branch in $(git remote-branches); do
        for base in $bases; do
            if git contains "$base" "$branch"; then
                if ! git contains "$branch" "$base"; then
                    branches_to_remove="$branches_to_remove $branch"
                    break
                fi
            fi
        done
    done

    if [ -n "$branches_to_remove" ]; then
        safegit branch -dr $branches_to_remove
    fi
fi
